STAT3 and neoplasm: EGFR mutations promote the invasion and brain metastasis of NSCLC cells by activating downstream signaling pathways such as the MET gene and STAT3 signaling pathway; Immune cells such as astrocytes and macrophages in the tumor microenvironment help tumor cells invade and colonize the brain by secreting inflammatory factors (such as IL-8, IL-6, etc.)and matrix metalloproteinases (such as MMP2, MMP9).